"Chris Hornbeck" wrote in message

On Thu, 20 Nov 2003 16:04:43 GMT, Carey Carlan
wrote:

Dithering smooths out the differences
between the 65,535 steps, making them as smooth as the 16 million
steps.

Dither is just noise, but noise has a special property in this case.
Although it can't smooth out differences, it can remove errors.

Dither doesn't remove the errors, it just makes them more palatable to the
ear.

Undithered quantization error is among the nastier, more unpredictable forms
of distortion around.

From http://www.pcabx.com/technical/bits44/index.htm (which has freely
downloadable .wav files that are practical examples of how dither changes
things)

Artifacts of improperly dithered quantization:

(1) Background noise level, from dither or quantization noise. Is it steady
or does it follow the intensity or tonality of the test tone?

(2) Intermittent spurious little whistles or "birdies" due to lack of dither
and the steady frequency change in the tone.

(3) Loss of low level signal due to lack of dither.

(4) Raspy distorted sound due to lack of dither.

OTOH, properly dithered quantization error sounds like background noise. We
even have some control over what the background noise sounds like. As the
signal goes down in amplitude, dither keeps it audible and recognizable even
when it is smaller than one quantization step.